The present invention relates to an arrangement for transforming a sequence of data packets into a regular or standard (time-division) multiplex for a data transmission system utilizing in one transmission direction the TDMA principle (Time-Division Multiple-Access), the transmission system being constituted by a network comprising a main station and sub-stations transmitting data packet-by-packet in time slots of the TDMA frames shared by and assigned to different sub-stations, the consecutive TDMA frames being transmitted to the main station to be transformed there into a regular multiplex in accordance with a predetermined frame, the arrangement being formed on the basis of a storage unit into which the data are entered.
Such an arrangement is described in the French Patent Application No. 86 17 864 filed on Dec. 19, 1986. It is accommodated in a system for transmitting data via a radio link of the point-multipoint type constituted by a network comprising a main station and a plurality of sub-stations. Such a configuration is often used to form a distributed telephone concentrator. In the direction from the main station to the sub-stations, the transmission is effected by broadcasting: the main station sends to all the sub-stations in accordance with a conventional (time division) multiplex mode. In the direction from the sub-stations to the terminal station the transmission is effected packet-by-packet and in accordance with the TDMA principle (Time-Division Multiple-Access): a sub-station does not send until a time slot has been assigned to it and in this time slot only this station can send. All the sub-stations are in synchronism with the main station and their transmission time bases are adjusted such that their distance (to the main station) is taken into account, to ensure that the sent data arrive without overlap at the main station. To that end guard periods are provided between all sent packets.
This system can thus be used to realize a telephone concentrator, in this case each packet sent by a sub-station which regroups a plurality of octets of a speech channel, represents a 64 kbit/s rate when the speech channel is encoded in accordance with the PCM method. But a rate of 64 kbit/s can be divided between several sub-stations for also retransmitting low-rate synchronous data links (for example 1200 bit/s). The French Patent Application mentioned in the foregoing describes an arrangement adapted to this type of transmission. In accordance with said application, to divide a channel between a plurality of data links which can originate from different sub-stations without the use of a large number of 64 kbit/s rates for the retransmission of low-rate data links, a frame and multi-frame structure is given to the TDMA transmission. Thus, a multi-frame is formed from n frames and the packets of one channel are assigned to a data link every n frame (n being higher according as the rate of the link is lower). At the main station, the sequence of packets of a channel conveying the different data links is transformed into a regular time-division multiplex in accordance with a predetermined frame. In the arrangement described, the transmission and the reception of the packets is particularized as follows.
On the one hand, in a sub-station, the transmission of a packet relating to a data link is effected in the frame or frames assigned to it via low-rate data transmission means (described in said Patent Application). The transmission of data is consequently effected with a delay caused by arranging the data into packets, this delay being the longer the lower the rate of the data link.
On the other hand, in the main station, the transformation or conversion of the sequence of packets for the reconstruction in a regular multiplex in accordance with a predetermined frame is effected when a complete multi-frame of packets has been received. This transformation then causes a delay which is a function of the position of the packets in the multi-frame, this delay can therefore be as long as the total duration of the multi-frame. Although this delay may not be too annoying as regards the data transmission, on the other hand it may be a disadvantage when it affects speech channels. Actually, in that case, this additional delay is added to the delays produced by the packetizing of the signal and the passage through the telephone network and may cause an increase of the echo path, such that this echo may become annoying for a telephone conversation.